[CapedCrusader]

How about this?

      var totalcount as number
      totalcount = 0
      foreach pick in hero where "thingid.skKnow"
          if (compare(lowercase(eachpick.field[domDomain].text),"science") = 0) then
            if (eachpick.field[trtFinal].value >= 3) then
              totalcount += 1
              endif
          endif
          if (compare(lowercase(eachpick.field[domDomain].text),"occult") = 0) then
            if (eachpick.field[trtFinal].value >= 3) then
              totalcount += 1
              endif
          endif
          if (compare(lowercase(eachpick.field[domDomain].text),"navigation") = 0) then
            if (eachpick.field[trtFinal].value >= 3) then
              totalcount += 1
              endif
          endif
        nexteach
      validif (totalcount >= 1)

A little clunky, I'll admit, but it should work. And if you wanted to check if it was two of them, change the (totalcount >= 1) to (totalcount >= 2), or 3 for all 3.